The overall goal of this project is to analyze the utility of metallic reference markers (implants) in improving our understanding of craniofacial growth and development. The availability of data from two longitudinal collections of patients with implants (n=35 and n=281) enables us to perform this analysis at the present time. When using the images of the implants to superimpose the jaws on x-ray films from two time points, one can study (1) mandibular growth and remodeling, (2) the changing positions of the mandible and maxilla with respect to the anterior cranial base, and (3) tooth development within each jaw. The first aim of this project is to compare four methods of superimposition, two of which require implants and two of which do not: (1) the standard method of classical orthodontics, (2) the "structural" method of Bjork, (3) the standard implant method, and (4) a computer-derived implant method. These comparisons will answer the following questions: (a) Does the use of implants in craniofacial studies lead to different answers on average and in individual cases than the same studies performed without implants? (b) Does Bjork's structural method of superimposition match the implant methods better than the standard method of classical orthodontics does? (c) Can we improve the analyses of implanted patients by having the computer derive superimpositions? The second aim of this project is to analyze the perceived stability within each jaw of the images of the implants. Least-squares techniques will be used to quantify the instability of the implants based on the longitudinal series of x-ray films. The utility of the implant superimpositions will be limited if the distances between the images of the implants within each jaw change over time. The third aim of this project is to demonstrate the utility of the implants for constructing confidence intervals for craniofacial parameters of interest. These confidence intervals will be intra-individual, i.e. will pertain to a given individual and be derived only from that individual's data. Thus, individuals with more consistent head positioning and better film quality could have tighter confidence intervals than other individuals. Least-squares techniques will enable the computation of these intervals. The methodology for construction of these confidence intervals should be of great utility to clinicians.